I think one of my platys is sick

[RunningOutOfIdeas]

I have 7 platys. Six are growing really well but one female is noticeably smaller than all the others. She has recently started hiding more. When I feed them, she comes up to the surface with all the others, looks like she is feeding but I think she is nibbling a little and spitting the food out.

I can't see anything obviously wrong with her. Any one have any ideas?

Have you got any water test results? How big is the tank? If there are no exterior symptoms then it could be a bacterial infection. Have you noticed any bullying?

I have a liquid test kit and check regularly. The results have been fine: ammonia and nitrite = 0, nitrates less than 20.

It is a 60L tank. I change 10 - 15L each week.

There was some bullying from one male until about 3 weeks ago. Then another male turned on him and they all seem to have settled down now.

Is there a treatment you would recommend for a bacterial infection?

This morning the fish is on the bottom of the tank. I need to put her out of her misery. How do I do this?

Oh, I just spotted this :( Sorry to hear about your fish. If you still need to euthanise her then clove oil is the most humane way. There are instructions here.

With bacterial infections I usually try something mild like melafix to start with, and if that doesn't work (most times it does if you catch it early) then antibiotics is the next step.